Multiple channel transmission system



May 31, 1932. I TAYLOR 1,861,370

MULTIPLE CHANNEL TRANSMISSION SYSTEM Filed Apg. 24, 1926 IN V EN TOR.

ATTORNEY Patented May 31, 1932 UNITED STATES PATENT OFFICE ALBERT H. TAYLOR, WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR, BY MESNE ASSIGNMENTS, TO WIRED RADIO, INQ, OF NEW. YORK, N. Y., A CORPORATION OF DELAWARE MULTIPLE CHANNEL TRANSMISSION SYSTEM Application filed August 24, 1926. Serial No. 131,209.

My invention relates broadly to signal transmission systems and more particularly to a multiple channel communication circuit employing the same transmitter.

One of the objects of my invention is to provide a circuit arrangement for a continuous wave transmitter by which a plurality of separate communication channels may be established without mutual interference.

Another object of my invention is to provide an intermediate circuit in a multiple channel transmitter by which energy at a plurality of frequencies may be transferred to the transmission system simultaneously and withoutinterference.

Still another object of my invention is to provide a system for coupling a plurality of piezo-electric crystal controlled oscillators with a transmission circuit forthe simultaneous operation thereof without mutual interference.

Other and further objects will be understood from the specification hereinafter following by reference to the accompanying drawing, in which the figure is a wiring diagram of a multiple channel communication system embodying the principles of my invention.

In my copending application Serial Number 30,252, filed May 14, 1925, I have described a two channel communication system employing modulated continuous waves. In my present invention I provide a transmitter employing pure continuous waves with a special intermediate circuit between the transmission circuit and the several oscillations for preventing mutual interference under conditions of simultaneous operation.

While not limited to any specific frequency, my'invention herein described finds-its most practical application at high frequencies. When the tuned circuits in various parts of a high frequency transmitter are considered, operating for instance, as a specifio example, at 4000 kilocycles, it will be noted that the action of these circuits will be substantially the same, as far as their ability to transfer energy from one part of the transmitter to another is concerned, at 4000 kilocycles, or at some other frequency differ,

ing only bya few kilocycles, say 4 kilocy cles. 4004 kilocycl'es with respect to circuits adjusted to 4000 kilocycles is only one-tenth of one per cent out of tune. The frequency of a master oscillator which is driving a power amplifier, and which in turn, is feeding in to an antenna or line wire transmissioncin cuit, can be varied a number of kilocycles Without seriously influencing the output of the antenna or transmission circuit. This is because of the fact that it takes a number of kilocycles to accomplish any considerable detuning. In other words, a power amplifier adjusted to a high frequency will pass a considerable band of kilocycles without serious loss. Taking advantage of this fact, I provide a master oscillator which can simultaneously develop two piezo-electric crystal controlled'frequencies. This master oscillator may be used in any of thewell known Ways to excite the grid of the power amplifier. The master oscillator is capable of de veloping either individually or simultaneously, two frequencies which do not differ from each other more than a small fraction of one per cent. a

, The transmitter affords, with the same power supply, same tubes, same coils and antenna system, two or more simultaneous channels of communication, and by varying the relative intensity of the two simultaneous frequencies in the master oscillator, the average energy of the transmitter can be ascertained at the several frequencies.

Referring to the drawing in more. detail the circuit illustrates a two-frequency master oscillator controlled by quartz crystals. 7 The two quartz crystals, marked Q1 and Q 2,

have contact plates above and below. Q l

controls the left-hand tube 2,- and Q, 2 con- V trols the right-hand tube 2. The chokes marked S1 and S-2 are sensitizing chokes of free wavelength considerably shorter than that corresponding to the crystal. The

chokes marked RFC are high frequency chokes through which the negative 0 voltage is fed to the grid electrodes 1 and l ofthe two tubes 2 and 2. Parallel plate feed from generator 3 is shown coming in through another set of the radio frequencychoke coils shown separate batteries.

represented at 4 and 4, although it will be understood that series feed may be employed when desirable.

The condensers marked C1 and C2 are respectively by-pass condensers for left and right-hand tubes 2 and 2. The plate circuit inductance of the left-hand tube is L1 plus a small portion of L. The plate circuit tuning for the left-hand tube is accomplished by variation of the condenser C3. The plate circuit of the right-hand tube consists of the inductance L2 plus a same small portion of inductance L. In other words, a small portion of inductance L in an intermediate circuit is common" to the two plate circuits of tubes 2 and 2. The plates are both supplied from the same high voltage generator 3, and the filaments may be supplied from the same filament battery although for purposes of illustration, I have The plate circuit of the right-hand tube is tuned by means of condenser Cl.

Oscillations corresponding to the frequency of Q,1 are developed in the plate circuit of the left-hand tube when the condenser C3 is adjusted to the correct point. This also holds true for the oscillation of the right-hand tube when the condenser C4 is adjusted to the correct point, but when the condenser C in the intermediate circuit is varied, it is found that the ammeter A records the summation effect of two oscillations of the two frequencies correspondingto the quartz crystals Q1 and Q,2. This comes about because a portion of the inductance L carries simultaneously the radio frequency component of both plate circuits. The currents of the two desired frequencies, therefore, circulate simultaneously in the circuit Keying of theseparate and simultaneous frequencies maybe accomplished in several different ways, such as by the use of a blockingvoltage on the grid or by opening the plate circuit, but it is found that there are small frequency changes brought about by most of the methods. By the arrangement disclosed in the diagram keyingris accomplished by a circuit which throws a. small capacity (about .002 microfarads for frequencies in the neighborhood of. 4000 kilocycles) between the grid and thefilament electrodes. This serves tosuppress the oscillations of the tube. A reversed contact relay orkey, is used to send out the frequency corresponding to the tube in question. In other "words, the signal is sent when the key is open and is stopped when the key closes. This arrangement has been found to leave the frequencies very constant whether they go out simultaneously or individually.

The system o-fkeying illustrated herein is intended particularly for high frequencies .to avoid all interference with the starting and stopping of oscillations of the piezo electric crystal control circuits. I have successfully keyed the crystal control circuits at a rate of 25 words per minute by the method described herein. In the diagram the separate circuits have been represented as controlled at K and K connected to condensers 6 and 6 with the grid electrodes 1 and l of the tubes 2 and 2. The keying circuits are disposed between the cathode and the grid of each of the tubes 2 and 2. Suitable biasing potentials for the operation of each of the tubes is supplied from a common source 7 through the radio frequency choke coils hereinbefore described.

The output of the intermediate circuit 5- is delivered to a suitable power amplification system represented at 8.

The input circuit of the .power amplifier connects across a selected portion of the inductance L through coupling condensers 9 and 10. The output circuit of the power amplifier is represented at 11 coupled to a suitable transmision circuit or antenna-ground system at 12 It will be understood that the transmission circuit of my invention as described herein is not limited to transmission of two frequencies but that a multiple number of frequencies may be employed following the principles of my invention.

lVhile I have described-my invention in one of its preferred embodiments, I desire that it be understood that modifications may be made and that no limitations upon the invention are intended other than are imposed by the scope-of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows: I I

l. A transmission system comprising a piezo-electric crystal controlled oscillation generator, a keying circuit comprising an interrupter and auelectrostatic capacity connected in' series, and said keying circuit being connected in parallel with the input circuit of said oscillation generator.

2. A transmission system comprising a piezo-electric crystal controlled oscillation generator, a keying circuit comprising an interrupter-and an electrostatic capacity connected in series, and said keying'circuit being connected to the input circuit of said oscillation generator.

3. 'A 7 transmission system comprising a piezo-electric crystal element, an oscillation generator controlled by said crystal element, and means including a circuit with a key and a condenser therein, said circuit being in shunt with said crystal element for varying the controlling influence of said crystal element in accordance with the signals to be transmitted. I v

4. A transmission system comprising a pluralityofpscillation generators each ineluding an electron tube and a piezoelectric crystal for controlling the frequency of oscillation thereof, a key and a condenser connected in series between the cathode and the grid of said electron tube and in shunt with said piezo-electric crystal, an output circuit for each of said generators, means for tuning each output circuit to a different frequency, and a tuned circuit common to said output circuits for establishing resonance simultaneously to the frequencies of said oscillation generators.

5. A transmission system comprising a plurality of oscillation generators each including an electron tube and a piezo-electric crystal for controlling the frequency of oscillation thereof, a key and a condenser connected in series between the cathode and the grid of said electron tube and in shunt with said piezo-electric crystal, an output circuit for each of said generators, and an amplifier having input and output circuits, said amplifier input circuit comprising a tuned circuit common to the output circuits of said osrcillation generators for establishing reso-' nance simultaneously to the frequencies of sand oscillation generators.

ALBERT H. TAYLOR. 

